title: Lipoproteins of slow-growing Mycobacteria carry three fatty acids and are N-acylated by apolipoprotein N-acyltransferase BCG_2070c.
abstract: BACKGROUND
  Lipoproteins are virulence factors of Mycobacterium tuberculosis. Bacterial lipoproteins are modified by the consecutive action of preprolipoprotein diacylglyceryl transferase (Lgt), prolipoprotein signal peptidase (LspA) and apolipoprotein N- acyltransferase (Lnt) leading to the formation of mature triacylated lipoproteins. Lnt homologues are found in Gram-negative and high GC-rich Gram-positive, but not in low GC-rich Gram-positive bacteria, although N-acylation is observed. In fast-growing Mycobacterium smegmatis, the molecular structure of the lipid modification of lipoproteins was resolved recently as a diacylglyceryl residue carrying ester-bound palmitic acid and ester-bound tuberculostearic acid and an additional amide-bound palmitic acid.
  
  
  RESULTS
  We exploit the vaccine strain Mycobacterium bovis BCG as model organism to investigate lipoprotein modifications in slow-growing mycobacteria. Using Escherichia coli Lnt as a query in BLASTp search, we identified BCG_2070c and BCG_2279c as putative lnt genes in M. bovis BCG. Lipoproteins LprF, LpqH, LpqL and LppX were expressed in M. bovis BCG and BCG_2070c lnt knock-out mutant and lipid modifications were analyzed at molecular level by matrix-assisted laser desorption ionization time-of-flight/time-of-flight analysis. Lipoprotein N-acylation was observed in wildtype but not in BCG_2070c mutants. Lipoprotein N- acylation with palmitoyl and tuberculostearyl residues was observed.
  
  
  CONCLUSIONS
  Lipoproteins are triacylated in slow-growing mycobacteria. BCG_2070c encodes a functional Lnt in M. bovis BCG. We identified mycobacteria-specific tuberculostearic acid as further substrate for N-acylation in slow-growing mycobacteria.
authors.affiliation: Institute of Medical Microbiology, University of Zurich, Gloriastrasse 30/32, CH-8006, Zurich, Switzerland. psander@imm.uzh.ch.
authors.forename: Juliane K
authors.initials: JK
authors.lastname: Brülle
authors.forename: Andreas
authors.initials: A
authors.lastname: Tschumi
authors.forename: Peter
authors.initials: P
authors.lastname: Sander
mesh_terms: D000107:Acetylation; D000217:Acyltransferases / Q000378:metabolism*; D019295:Computational Biology; D005227:Fatty Acids / Q000378:metabolism*; D055786:Gene Knockout Techniques; D008074:Lipoproteins / Q000737:chemistry / Q000378:metabolism*; D009163:Mycobacterium bovis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D005227:Fatty Acids; D008074:Lipoproteins; D000217:Acyltransferases; C068902:apolipoprotein N-acyltransferase